Conventional heat sinks are arranged and configured to include a base plate and a plurality of cooling fins extending from the base plate and spaced apart by a plurality of grooves. During use, the base plate disperses heat generated by an electronic device, a motor, or any other system, and air is blown through the grooves over the cooling fins. Typically, each of the cooling fins and grooves are uniform in size and designed to optimize cooling for any given application. In certain applications, however, vibrations generated by the system can transfer to the cooling fins and generate an unpleasant sound.
In one known application of a heat sink, a centrifuge includes a rotor and a variable speed electric motor adapted to drive the rotor via a drive shaft. The motor includes a motor housing that includes a generally cylindrical member constructed of aluminum, and which contains the stator and winding coils of the motor. During use, the motor generates heat and therefore the motor housing serves as a heat sink and is equipped with a plurality of cooling fins, across which air is blown to cool the system. The fins are of generally uniform dimension and are separated by grooves of generally uniform dimension. Such a design effectively cools the motor, but can generate an unpleasant sound at certain speeds. This is due to the fact that all of the fins are the same size and shape, and therefore, they all share a common resonant, fundamental, and/or harmonic frequency. More specifically, at certain speeds the vibrations in the system simultaneously excite the fundamental, resonant, and/or harmonic frequencies of the fins, and this produces aloud unpleasant sound. Testing has illustrated that when the motor of the above-described centrifuge accelerates and decelerates near a speed of approximately 83,000 RPM, a high pitch whine is produced. This whine is also produced at steady state operation near 83,000 RPM, but with slightly less magnitude.